Oral creatine (Cr) supplementation has been proposed to be a treatment for several myopathies. Oral ingestion of Cr in the form of meat and fish supplements is known to increases the whole body Cr pool. Ingestion of 20-30g Cr/day for several days can lead to greater than a 20% increase in total muscle Cr content, of which 20-30% is in the form of phosphocreatine (PCr). Moreover, Cr ingestion has been shown to significantly increase the amount of work that can be performed during repeated bouts of maximal exercise with decreased rates of plasma ammonia accumulation. During brief periods of high ATPase flux, PCr hydrolysis can account for greater than 80% of total ATP synthesis. This suggests that Cr supplementation results in more efficient ATP-resynthesis, probably as a consequence of an increase in high energy phosphate (PCr) availability. To determine the effect of Cr supplementation on contractile and metabolic properties of the gastrocnemius muscle, we carried out a double-blind, cross over study on 6 male, collegiate athletes. Three subjects ingested 0.4 g Cr monohydrate whereas the rest ingested 0.4 g glucose per kg body weight daily, for a total of 5 days. Following a month recovery, the treatments were reversed. MRS and Biodex measurements were performed following the 5th day of Cr or placebo ingestion. Changes in peak torque, power output and relative fatigue were measured during repeated bouts of isokinetic plantar flexion (60~/s) separated by 2 min of recovery. Changes in basal metabolic rate, ATP cost per contraction, and aerobic ATP synthesis rates were measured using 31P-MRS during and following direct muscle stimulation with and without blood flow. In addition, oxidative and anaerobic ATP synthesis rates were followed during repeated bouts of maximal voluntary exercise.